Ciclazindol

Two electrode voltage clamp and single channel recordings were used to investigate the actions of various ATP‐sensitive K+ (KATP) channel inhibitors on cloned KATP channels, expressed in Xenopus oocytes and HEK 293 cells.Oocytes expressing Kir6.2 and SUR1 gave rise to inwardly rectifying K+ currents following bath application of 3 mM sodium azide. Inside‐out recordings from non‐azide treated oocytes demonstrated the presence of KATP channels which were activated by direct application of 3 mM azide and 0.1 mM Mg‐ATP.Tolbutamide inhibited azide‐induced macroscopic Kir6.2‐SUR1 currents, recorded from Xenopus oocytes, with an IC50 value similar to native KATP channels. Ciclazindol and englitazone also inhibited these currents in a concentration‐dependent manner, but with relative potencies substantially less than for native KATP channels.Single channel currents recorded from inside‐out patches excised from oocytes expressing Kir6.2‐SUR1 currents were inhibited by tolbutamide, Mg‐ATP, englitazone and ciclazindol, in the absence of azide, with potencies similar to native KATP channels. In the presence of azide, Kir6.2‐SUR1 currents were inhibited by englitazone and tolbutamide but not ciclazindol.Single channel currents derived from Kir6.2Δ26, expressed in HEK 293 cells, were inhibited by ciclazindol and englitazone irrespective of the absence or presence of SUR1.In conclusion, heterologously expressed Kir6.2 and SUR1 recapitulate the pharmacological profile of native pancreatic β‐cell KATP channels. However, currents induced by azide exhibit a substantially reduced sensitivity to ciclazindol. It is likely that ciclazindol and englitazone inhibit KATP currents by interaction with the Kir6.2 subunit.British Journal of Pharmacology (2000) 130, 857–866; doi:10.1038/sj.bjp.0703395

Vasodilator responses to anandamide (arachidonylethanolamide) and potassium ions were compared with those mediated by endothelium-derived hyperpolarizing factor (EDHF) in guinea-pig isolated basilar artery contracted with prostaglandin F2alpha. In this artery, EDHF-mediated responses can be evoked by acetylcholine in the presence of both indomethacin (10 microM) and NG-nitro-L-arginine (0.3 mM). In endothelium-denuded arterial segments, which failed to respond to acetylcholine, anandamide was still able to evoke a complete relaxation. Anandamide (10 microM) did not affect the resting membrane potential, whereas acetylcholine (10 microM) hyperpolarized the smooth muscle cells by 23 mV in the presence of indomethacin and NG-nitro-L-arginine. Pre-treatment with capsaicin (10 microM) or resiniferatoxin (0.1 microM) abolished the anandamide-induced relaxation, but had no effect on the EDHF-mediated relaxation induced by acetylcholine. Treatment with a mixture of the calcium-sensitive potassium channel inhibitors, apamin and charybdotoxin, which abolishes EDHF-mediated relaxation in this artery, did not affect the relaxation evoked by anandamide. The additional presence of glibenclamide or ciclazindol, inhibitors of ATP-sensitive and voltage-dependent potassium channels, also had no effect on the anandamide-induced relaxation. Increasing the potassium ion concentration by 2-10 mM induced inconsistent vasodilator responses. However, re-admission of potassium ions to preparations incubated in potassium-free solution elicited almost complete and sustained relaxations. A short incubation period with ouabain (10 microM for 10 min) or cooling (18-22 degrees C) abolished these responses, whereas the acetylcholine-induced relaxation in the presence of indomethacin and NG-nitro-L-arginine was unaffected (ouabain) or partially reduced (cooling). The anandamide-induced relaxation was also abolished by ouabain and cooling. Furthermore, ouabain inhibited the vasodilator response to capsaicin, but not that to calcitonin gene-related peptide (CGRP), and per se evoked a release of CGRP from the artery. The gap junction uncoupler, 18alpha-glycyrrhetinic acid (100 microM), affected neither the EDHF-mediated relaxation induced by acetylcholine nor the vasodilator responses to anandamide and potassium ions. Thus, EDHF-mediated vasorelaxation in the guinea-pig basilar artery does not seem to involve Na+/K+-ATPase, sensory nerves or gap junctions. These results indicate that EDHF is neither anandamide nor potassium ions in this artery.